Restore netcdf4 to pyproject dependencies list

This change restores the 'netcdf4' package to the list of dependencies in the
pyproject.toml file. This corrects and error introduced in PR #132 when
'netcdf4' was replaced with 'h5netcdf'. Subsequent testing in that PR revealed
that we presently can only use 'h5netcdf' for dataset reading and must continue
to use 'netcdf4' for dataset writing. So, both packages are dependencies.

pyproject.toml

@@ -45,6 +45,7 @@ dependencies = [
     "dask",
     "flox",
     "h5netcdf",
+    "netcdf4",
     "pyyaml",
     "rich",
     "structlog",